Show widget file path in inspector

[khanak0509]

Issue #9922
This PR fixes issue #9922 where the new Flutter Inspector didn’t show the widget’s file path like the legacy inspector did. You could select a widget and see layout/properties on the right, but there was no main.dart:line:column anywhere — the summary tree is loaded without full details, so creationLocation never showed up in the UI.

How I fixed it:
Basically, when a widget is selected we fetch a small details subtree for just that node, read creationLocation, and show filename.dart:line:column above the properties tabs. The widget tree load stays the same so we don’t pull full details for every node.

before --

after --

Pre-launch Checklist

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[gemini-code-assist]

Code Review

This pull request introduces the display of a widget's creation source location (file name, line, and column) in the DevTools Inspector. It updates the InspectorController to fetch this information from the details subtree, adds a new WidgetCreationLocationHeader widget to display it, and includes corresponding unit tests. The review feedback highlights a potential crash if the controller is disposed during an asynchronous operation, suggests a defensive null check for the node ID in getDetailsSubtree, and recommends using a null-assertion operator to satisfy strict null safety in the creation location header.